1. Field of the Invention
The present invention relates generally to optical recording media and methods for recording and reproducing information therein.
2. Description of the Prior Art
Optical recording media, such as magneto-optical disks, typically include guide grooves (or pregrooves) for tracking which are preformed in a spiral or concentric pattern. Data is recorded by means of the magneto-optical effect in recording tracks either within the guide grooves or in the lands between adjacent guide grooves. In general, address information and data are alternately recorded on the recording tracks. The address information provides a means of controlling the recording and reproducing of the data on a block-by-block or sector-by-sector basis.
Japanese Patent Publication No. 63-87682 (1988) concerns a technique in which wobbling tracks used for detecting tracking errors are recorded after frequency modulation by a time code. In accordance with this technique, a sinusoidal carrier signal of, for example, 22.05 kHz, is frequency modulated by a time code signal having a frequency which is sufficiently low in comparison with the carrier wave to form wobbling tracks. Tracking error signals are produced upon reproduction and the time code is demodulated to produce position information.
However, this technique does not provide the ability to achieve clocking of the recorded signals in the track by means of the track wobbling signals. Moreover, the wobbling signals are not only susceptible to noise but also low in extraction accuracy since timing information is inserted only between blocks of data. Accordingly, they can be decoded only by reading a complete block and, thus, it is difficult to achieve correct positioning.
In addition, in order to read the principal information (such as magneto-optical signals) recorded in the track along its length, it is necessary to provide a relatively long preamble at the leading edge of the recorded principal information in order to regenerate clock signals stored therein which are necessary for reproducing the main information.